Production of bulked ply yarns of balanced tensile strength and the yarn



1964 H. CROUZET PRODUCTION OF BULKED PLY YARNS OF BALANCED 'rsnsms STRENGTH AND THE YARN Filed Dec. 19, 1960 Inventor HENRI CROUZET tlorn 3,117,411) narrow or BULKED rLY YAnss or arts-no TENSHLE STRENGTH AND 'riia Henri irouzet, Reanne, France, assignor to Moulinage et Retorderie de Chavanoz, Chavanoz (isere), France, a

body corporate Filed Rec. 19, 1960, Sea". No. 76,855 7 iairns. Ci. 57--14t3) This invention relates to improvements in the production of bulked yarns, by a process involving high twisting of the yarn, setting it and untwistin-g.

it is well known to produce bulked yarns by a multistage process in which the yarn is first subjected to high twist, the twist is set, for example by means of dry heat, and the yarn is then untwisted. Other processes may follow such as a further setting or shrinking of the yarn. As an alternative to this process a continuous process has been devised and has met with considerable commercial acceptance, which comprises running the yarn through a heat-setting zone then through a false twisting device so disposed with reference to the heat-setting zone that the twist runs back along the yarn into the setting zone and finally, after the twist has been removed on the far side of the false twister, leading the yarn to a take-up device. It is further known to combine two such yarns one of which has been subjected to high twist in the S direction and the other to the same high twist in the Z direction so as to produce an assembly which is to some extent compensated against residual twist.

For any given type of treatment and particularly temperature of heat-setting, the breaking strength of a synthetic yarn treated as above is a function of the temporary twist imparted to the yarn. With increasing twist the tensile strength at first decreases slowly and, after a certain degree of twist, decreases very rapidly. The accompanying drawing illustrates this eiiect.

FEGURE 1 shows the relationship between the tensile strength and the twist imparted to nylon yarn. Acceptable bulk in the resulting yarn is only obtainable at about the point A on the curve, i.e. at a degree of twist which is very near to the point at which the slope of the curve changes sharply. Beyond the zone AB the extensibility remains high but the tensile strength is too low to be accc-ptable.

it has been observed that in any of the above processes, Where the starting yarn has an initial twist, for example 0.5 turn per inch, a bulked yarn obtained by applying high twist in the same direction as the initial twist of the yarn has a lower tensile strength than has a bulked yarn obtained by applying high twist in the reverse direction to that of the initial twist.

FIGURE 2 represents the two cases of applying a temporary twist in these two different directions, the two ends being subjected to the same high twist and the same setting temperature. It will be noted that one curve is substantially displaced with reference to the other and that, using any given twist, the yarn in which that high twist has been inserted in the same direction as the initial twist in the yarn consistently has the lower tensile strength. The extensibility of an assembly of the two yarns is a function of ie mean of the twists applied to the two separate ends.

According to the present invention the extensibility of such an assembly is increased by applying to one end of the yarn a different high twist from that applied to the other so as to obtain substantially the same tensile strength in the two bulked yarns. Thus, referring to FIG. 2, the one end, in which the twist is inserted in the same direction as the initial twist, is twisted to a point A on Patented Jan. 14f, lQtii the curve corresponding with a twist T. The other end of the same yarn is given a higher temporary twist T in the reverse direction from that of the initial twist and the bulked yarn so obtained has a tensile strength corresponding with the point A on the curve, i.e. substantially the same as that of the first bulked yarn. When two such bulked yarns are assembled together the average twist is greater than T and the assembly has a higher extensibility than has an assembly of two similar yarns made by applying equal high twist in the S and 2 directions.

E or example, starting with a 6, 6 nylon yarn of 7 0 denier and an initial twist of 0x5 turn per inch 2 twist, it one end of the yarn is given and S twist of 69 turns per inch and the other a Z twist of 69 turns per inch, the average of the two is, of course, still 69 turns per inch and the extensibility of the assembly of the two bulked yarns is found to be 208%. The tensile strength of the bulked yarn given S twist is 98 grants and that of the yarn given Z twist is grams.

On the other hand according to the present invention the S and Z twists applied to the two separate ends of the initially twisted yarn are so related that the resulting bulked yarns have a substantially equal tensile strength. For example, if as before the Z twist amounts to 69 turns er inch giving a tensile strength in the bulked yarn of 80 grams, the S twist is increased to 73 turns per inch and the bulked yarn therefrom has the same tensile strength. The elongation of the resulting assembly is 2.15%, the average twist being 7i turns per inch.

The invention may be applied either with the discontinuous method of high twisting, setting and untwisting, or with the continuous method using a false twister and it may be applied to any heat-settable yarn in addition to the 6, 6 nylon yarn specified and particularly to heat-settable synthetic fibres. For such other yarns, the numerical data will obviously be different but the necessary data can readily be obtained by drawing curves similar to those of FIGURES 1 and 2.

In each case the two yarns may be assembled by applying a light doubling twist.

I claim:

1. Process for the production of an assembly of bulked yarns of a synthetic polymer, comprising applying high S and Z twist respectively to separate ends of a yarn having an initial low twist, fixing the high twist and then untwisting, the 8 and 2 high twists being of sufiiciently different degree that the tensile strengths of the resulting separate bulked yarns are substantially equal, then associating the two yarns together.

2. Process according to claim -1 wherein in each case the high twist applied is such as to bring the yarn near to the point where a curve relating the tensile strength of the bulked yarn to the temporary twist undergoes a sudden change of direction.

3. Process for the production of an assembly of bulked yarns of a synthetic polymer, comprising providing separate ends of a yarn having an initial low twist, bulking said ends by false twisting in the S and 2 directions to differential levels, each in a continuous run while allowing the false twist to run back to a heat-setting zone, and associating the bulked yarns together, the S and 2 high twists being of sufliciently different degree that the tensile strengths of the separate bulked yarns are substantially equal.

4. Process acording to claim 3 wherein in each case the high false twist applied is such as to bring the yarn near to the point where a curve relating the tensile strength of the bulked yarn to the temporary twist undergoes a sudden change of direction.

5. Process for the production of an assembly of bulked yarns of a synthetic polymer, comprising providing separate ends of a nylon yarn having an initial low twist, bulking said ends by false twisting one end in the 8 direction and the other end in the 2 direction, the end which is twisted in the same direction as the initial low twist being of a suifieiently lesser degree than the end which is twisted in the opposite direction that the tensile strength of said end is substantially equal to the other end, said differential twists being applied in a continuous run while allowing the false twist to run back to a heatsetting zone, and associating the bulked yarns together.

6. Process according to claim 5 where-in in each case the high false twist applied is such as to bring the yarn near to the point where a curve relating the tensile strength of the bulked yarn to the temporary twist undergoes a sudden change of direction.

7. An assembly of bulked yarns of a synthetic polymer, the filaments of each bulked yarn having a helical form, due to the filaments having been set while the yarn is highly twisted, the helices in the two yarns being in opposite directions, and the yarns having a residual low twist both in the same direction, the ends of the assembly having differential levels of twist whereby the tensile strengths of said ends are substantially equal.

References Cited in the file of this patent FOREIGN PATENTS 1,082,461 France June 16, 1954 1,130,364 France Sept. 24, 1956 791,610 Great Britain Mar. 5, 1958 

7. AN ASSEMBLY OF BULKED YARNS OF A SYNTHETIC POLYMER, THE FILAMENTS OF EACH BULKED YARN HAVING A HELICAL FORM, DUE TO THE FILAMENTS HAVING BEEN SET WHILE THE YARN IS HIGHLY TWISTED, THE HELICES IN THE TWO YARNS BEING IN OPPOSITE DIRECTIONS, AND THE YARNS HAVING A RESIDUAL LOW TWIST BOTH IN THE SAME DIRECTION, THE ENDS OF THE ASEMBLY HAVING DIFFERENTIAL LEVELS OF TWIST WHEREBY THE TENSILE STRENGTHS OF SAID ENDS ARE SUBSTANTIALLY EQUAL. 